Nociceptors/Pain

Question 1

Polynodal Nociceptors

Answer 1

C fibers respond to wide variety of intense mechanical stimuli, more responsible for diffuse/dull/aching/burning pain and delayed response

Question 2

Adelta Fibers

Answer 2

Larger and faster conducting, responsible for immediate “ouch” to more limited range of stimuli

Question 3

3 Kinds of Pain

Answer 3

Nociceptive
Neuropathic/genic
Psychogenic

Question 4

5 Activations of Nociceptors

Answer 4

a) K+ depols nerve terminals direclty
b) H+ open acid sensing ion channels that lets Na enter
c) ATP activates P2X cation channel
d) Bradykinin stimulates GPCRs
e) Heat activates unique temp-dependent TRPV1 cation channels

Question 5

Plasma Kininogen

Answer 5

Torn capillaries release, induces bradykinin synth

Question 6

Hyperalgesia

Answer 6

Increased lingering pain from tenderness/inflammation of tissues

Question 7

Axon Reflex

Answer 7

APs from Adelta and Cs branch in SC to activate neurons that send signals back out to periphery to release sensitizing substances like Substance P, NGF, 5HT, PGs, leukotrienes, CGRP, etc

Question 8

Substance P

Answer 8

Released in periphery to sensitize nociceptor nerve endings and induce mast cells to release histamine

Question 9

Resolvins

Answer 9

PG metabolites hours later that resolve rather than promote inflammation. Asprin promotes their synthesis so it acts as a double whammy

Question 10

Projection Neurons

Answer 10

Receive pain in dorsal root from pain fibers and decussate/rise up spinothalamic tract

Question 11

Anterolateral System (ALS)

Answer 11

Spinothalamic tract and its collaterals given off in brain stem

Question 12

2 Parallel Pathways for Pain

Answer 12

Both synapse in dorsal column and rise up spinothalamic tract contra, but one goes through thalamus to appropriate sensory cortex w/ detailed pain discrimination info. Other sends axons to parabrachhial nucleus and reticular formation in pons/medulla/thalamus and appears to carry affective or motivational aspects of pain - doesn’t even distinguish locations

Question 13

Third Pain Pathway

Answer 13

Carries visceral pain and rises up ipsilateral dorsal column

Question 14

Brown-Sequard Syndrome

Answer 14

Nerves damaged on one side of spinal cord, so you lose temp/pain from contra side and touch/proprio from ipsi

Question 15

Gate Theory vs. Allodynia

Answer 15

Aalpha/beta touch Rs can stimulate inhibitory interneurons on pain projection neurons or stimulate actual projection neuron

Question 16

Endogenous Opioids

Answer 16

Mainly Enkephalins and endorphins, peptide NTs that suppress ALS neurons at various points as pain neg feedback

Question 17

Central Sensitization

Answer 17

Prolonged EPSPs from C fibers cause hyperalgesia or allodynia similar to learning/memory, where touch can cause pain. Can cause post-surgical problems

Question 18

Mu-Opioid R

Answer 18

GPCR that opens K+ channels to hyperpolarize neuron. Stimulated by morphine

Question 19

Neuropathic Pain

Answer 19

Damaged nervous tissue releases ATP which stimulates microglia. These produce BDNF which converts GABA signals from inh to excitatory, opening up pain pathways. Morphine stimulates these microglia somehow so it is bad for neuropathic pain